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Fuse and Cable selection for PFC bank

Fuse and Cable selection for PFC bank

Fuse and Cable selection for PFC bank

(OP)

Hi there.

Recently our PFC bank cables got overloaded and eventually failed. The cables emanate from the 3.3Kv bus bars and terminate at the PFC yard via a duct. The specs of the PFC bank are as follows; Voltage=3.3Kv, PFC bank rating=2.8Mvar and it is required to correct the power factor to 0.85. The cables to the PFC yard are two 150mm^2 capable of carrying 720A. So what i want to know is if the cable are adequate for the task. Further more i wolud like to know how to calculate (procedure) the rating of the fuses protecting correction capacitors.

RE: Fuse and Cable selection for PFC bank

Necr,

You need to look at the impact of harmonics on the overloading of cables / capacitors as well.

RE: Fuse and Cable selection for PFC bank

The capacitor current at rated voltage and with no harmonics can be determined by:

(Mvar x 1000)/kV/sqrt(3)

(2.8 x 1000)/3.3/sqrt(3) = 489 amps

This assumes a three-phase capacitor bank and that the voltage is 3.3 kV phase-to-phase.

If the voltage is higher than the capacitor voltage rating, actual Mvar will be higher than rated (proportional to square of the voltage).  You may have a harmonic resonance with the source which causes high harmonic voltages and currents in the capacitor.

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